The present invention relates to an inkjet printing apparatus and a preliminary discharge control method.
An inkjet printer forms an image by discharging an ink droplet from a discharge orifice formed in a printhead and sticking the discharged ink droplet onto a printing sheet.
A printhead usually has a plurality of discharge orifices. If a discharge orifice not frequently used is present in these discharge orifices during printing, the ink viscosity in this discharge orifice rises owing to water evaporation to clog this discharge orifice. To avoid this phenomenon, ink droplets corresponding to a predetermined number of dots are discharged, at predetermined time intervals or in accordance with the calculated use ratios of the ink discharge orifices, while printing is executed, into an ink receptor (to be referred to as a preliminary discharge receptor) formed outside the scanning region of the printhead, thereby holding the state of each discharge orifice and its vicinity constant. This operation is called a preliminary discharge operation.
FIG. 7 is a perspective view showing an outline of the arrangement of a conventional inkjet printer.
Referring to FIG. 7, reference numeral 101 denotes a printing sheet; 102, an automatic sheet feeding mechanism which feeds stacked printing sheets one by one into the printer and, as printing progresses, discharges each printing sheet forward (in the direction of an arrow); 103, a carriage; and 104, an ink cartridge containing a printhead which is so mounted as to discharge ink downward (toward the printing sheet).
The carriage 103 on which the ink cartridge 104 is mounted moves back and forth parallel to the printing sheet in a direction perpendicular to the conveyance direction of the printing sheet. An image is formed by discharging ink stored in the ink cartridge 104 toward the printing sheet.
Reference numeral 105 denotes a carriage motor; and 106, a driving belt. The carriage 103 is interlocked with the carriage motor 105 by the driving belt 106. When the carriage motor 105 is driven forward and backward, the carriage 103 moves forward and backward. Guide shafts 107 and 108 for mounting the carriage 103 support the forward and backward movements of the carriage 103 mounting the ink cartridge 104.
Reference numerals 109 and 110 denote preliminary discharge receptors. In a preliminary discharge operation, the carriage 103 moves to a position above the preliminary discharge receptor 109 or 110, and the printhead discharges ink droplets corresponding to a predetermined number of dots.
In this conventional inkjet printer, as can be seen from FIG. 7, a preliminary discharge receptor is generally formed on one or both sides of the scanning region of the printhead. When a preliminary discharge operation is to be executed, the printhead is moved from the printing end position to the position above the preliminary discharge receptor.
FIG. 8 is a schematic view showing the control of a printing operation and a preliminary discharge operation in this conventional inkjet printer.
As shown in FIG. 8, when an image such as xe2x80x9cA . . . Axe2x80x9d is to be printed on the printing sheet 101, the carriage 103 mounting the printhead explained in FIG. 7 scans within the range of a line 301 from a point x to a point y. This line 301 is made up of a printing region in which an image is formed by discharging ink onto the printing sheet, and acceleration (deceleration) regions a and b. To form an image in the printing region, the carriage 103 must be driven at a constant speed. When the carriage 103 is at rest at a point 302, this carriage 103 is accelerated in the region a to move at the constant speed from a point 303. Also, to stop the carriage 103, which has moved at the constant speed to a point 304, at a point 305, this carriage 103 is decelerated in the region b.
When the image is to be printed by moving the carriage 103 in the opposite direction from the point y to the point x, the region b is an acceleration region, and the region a is a deceleration region. Therefore, printing region+region a+region b is the carriage moving range corresponding to a printing operation of one scan.
On the other hand, when a preliminary discharge operation is to be executed, the carriage 103 is moved to the position above the preliminary discharge receptor 109 or 110 to discharge ink. That is, when preliminary discharge is to be performed for the preliminary discharge receptor 109, the carriage 103 is moved to a point 307. A region d indicates a moving region from the carriage stop position to the preliminary discharge receptor 109. When preliminary discharge is to be performed for the preliminary discharge receptor 110, the carriage 103 is moved to a point 306. A region c indicates a moving region from the carriage stop position to the preliminary discharge receptor 110.
In the above prior art, however, if the width of the printing sheet is smaller than the maximum width of the scanning region, the actual scanning region of the printhead narrows in accordance with the width of the printing sheet. This increases the moving distance from the end of the scanning region to the preliminary discharge receptor when a preliminary discharge operation is to be performed. This undesirably prolongs the printing execution time.
FIG. 9 is a schematic view showing the control of a printing operation and a preliminary discharge operation of the conventional inkjet printer, when the width of a printing sheet is much smaller than the scan enable region. As is apparent from the comparison of FIGS. 8 and 9, the width of a printing sheet 400 is much smaller than the scan enable region shown in FIG. 8.
When an image such as xe2x80x9cA . . . Axe2x80x9d is to be printed on this printing sheet 400, the scanning range of the carriage 103 mounting the printhead explained in FIG. 7 is the range indicated by a line 401 from a point xxe2x80x2 to a point yxe2x80x2. This line 401 is made up of a printing region in which an image is formed by discharging ink onto the printing sheet, and acceleration (deceleration) regions axe2x80x2 and bxe2x80x2. To form an image in the printing region, the carriage 103 must be moved at a constant speed. When the carriage 103 is at rest at a point 402, this carriage 103 is accelerated in the region axe2x80x2 to move at the constant speed from a point 403. Also, to stop the carriage 103, which has moved at the constant speed to a point 404, at a point 405, this carriage 103 is decelerated in the region bxe2x80x2.
When the image is to be printed by moving the carriage 103 in the opposite direction from the point yxe2x80x2 to the point xxe2x80x2, the region bxe2x80x2 is an acceleration region, and the region axe2x80x2 is a deceleration region. Therefore, printing region+region axe2x80x2+region bxe2x80x2 is the carriage moving range corresponding to a printing operation of one scan.
When a preliminary discharge operation is to be executed, the carriage 103 is moved to the position above the preliminary discharge receptor 109 or 110 to discharge ink. That is, when preliminary discharge is to be performed for the preliminary discharge receptor 109, the carriage 103 is moved to a point 407. A region dxe2x80x2 indicates a moving region from the carriage stop position to the preliminary discharge receptor 109. When preliminary discharge is to be performed for the preliminary discharge receptor 110, the carriage 103 is moved to a point 406. A region cxe2x80x2 indicates a moving region from the carriage stop position to the preliminary discharge receptor 110.
As can be seen by comparing FIGS. 8 and 9, the width of the printing region decreases because the width of the printing sheet decreases. However, since the position of the preliminary discharge receptor 109 remains unchanged, the region dxe2x80x2 shown in FIG. 9 which is the moving region, from the carriage stop position to the preliminary discharge receptor 109, for performing a preliminary discharge operation is longer than the region d shown in FIG. 8. Therefore, although the printing region is narrowed, the carriage moving distance necessary to execute a preliminary discharge operation during a printing operation increases. This requires an extra time whenever a preliminary discharge operation is performed, prolonging the time to the completion of the printing operation.
Accordingly, it is an object of the present invention to provide a printing apparatus and preliminary discharge control method capable of minimizing the influence of a preliminary discharge operation on printing and keeping a short printing time.
According to one aspect of the present invention, the foregoing object is attained by providing an inkjet printing apparatus for printing on a printing medium by discharging ink, on the basis of printing data, from a printhead mounted on a carriage which moves back and forth on the printing medium. The apparatus includes preliminary discharge control means and preliminary discharge position designating means. The preliminary discharge control means controls the printhead to perform preliminary discharge, by which no printing is performed, between scanning actions of the carriage. The preliminary discharge position designating means designates a position at which the preliminary discharge is controlled by the preliminary discharge control means to be performed by the printhead. The preliminary discharge position designating means variably designates a preliminary discharge position, which is a predetermined distance away from an edge of the printing medium, as the position at which the preliminary discharge is to be performed, in accordance with a position of the edge of the printing medium.
The printing is desirably performed by forward and backward scans of the printhead.
The apparatus can further comprise an ink receptor for receiving ink discharged by preliminary discharge by the preliminary discharge control means, the ink receptor having a length not less than the length of a scanning range of the printhead. Alternatively, the apparatus can further comprise a plurality of ink receptors for receiving ink discharged by preliminary discharge by the preliminary discharge control means, in accordance with the width of the printing medium in the scanning direction.
The apparatus desirably further comprises sensing means for sensing an edge of the printing medium.
The preliminary discharge position designating means can designate a preliminary discharge position such that preliminary discharge is performed in a position separated a predetermined distance from the position of an edge of the printing medium, regardless of this edge position of the printing medium. The designated predetermined distance when the ink discharge frequency of the printing is relatively high is desirably made longer than that when the ink discharge frequency is relatively low.
When performing preliminary discharge after printing in a forward or backward scanning direction, the preliminary discharge control means desirably so controls the printhead as to move in the forward or backward scanning direction, after the printing is completed, and to perform a preliminary discharge operation.
The preliminary discharge position designating means can designate a preliminary discharge position in accordance with information about an edge of the printing medium sensed by the sensing means after the printing is performed.
The apparatus desirably further comprises storage means which, when preliminary discharge is to be performed after the printhead prints in a first direction of the forward and backward scans of the printhead, stores information about an edge of the printing medium sensed by the sensing means after the printing is completed, and, when preliminary discharge is to be performed after the printhead prints in a second direction opposite to the first direction, stores information about an edge of the printing medium sensed by the sensing means after the printing is completed.
The preliminary discharge control can be so performed that the preliminary discharge is performed, while the printhead is scanning, in a position farther from the printing medium than the position designated by the preliminary discharge position designating means, or that the preliminary discharge is performed before or after the scanning directions are switched.
Preferably, the printhead is an inkjet printhead for discharging ink by using thermal energy, and comprises an electrothermal converter for generating thermal energy to be applied to ink.
According to another aspect of the present invention, the foregoing object is attained by providing a preliminary discharge control method of an inkjet printing apparatus for printing on a printing medium by discharging ink, on the basis of printing data, from a printhead mounted on a carriage which moves back and forth on the printing medium. The method includes a preliminary discharge position designation step of designating a position at which preliminary discharge, by which no printing is performed, is performed between scanning actions of the carriage and a preliminary discharge control step of controlling the printhead to perform the preliminary discharge. The preliminary discharge position designation step variably designates a preliminary discharge position, which is a predetermined distance away from an edge of the printing medium, as the position at which the preliminary discharge is to be performed, in accordance with the position of the edge of the printing medium.
In accordance with the present invention as described above, when an inkjet printing apparatus for printing on a printing medium by discharging ink, on the basis of printing data, from a printhead mounted on a carriage which moves back and forth on the printing medium is to perform preliminary discharge, a position at which preliminary discharge, by which no printing is performed, is performed between scanning actions of the carriage is designated in accordance with the position of an edge of the printing medium in the scanning direction, and the printhead is caused to perform the preliminary discharge.
The invention is particularly advantageous since preliminary discharge can be performed in a designated position regardless of the width of a printing medium.
Accordingly, even when the width of a printing medium is smaller than the maximum width of a carriage scanning region, preliminary discharge can be performed with a minimum necessary carriage movement, without moving the carriage to an edge of the carriage scanning region unlike in conventional apparatuses. This can minimize the time for the carriage movement and therefore minimize the printing execution time.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.